1. Field of the Invention
The present invention relates to a technique of generating measurement information regarding measurement points on a semiconductor wafer and determining positions of the measurement points based on the measurement information.
2. Description of the Related Art
Semiconductor wafers are subjected to various tests with a variety of measurement devices in its manufacturing process. In the course of a specific measurement, a positioning process (alignment process) is carried out to position a measurement probe (such as an optical element or an electrode) precisely at a predetermined measurement point on a wafer.
In some cases, it is desired to carry out a certain measurement with a plurality of measurement devices. Each wafer can, however, take various orientations and positions in the respective measurement devices, and the coordinates of measurement points on the wafer will have different values in different measurement devices. It is accordingly impossible to commonly apply the same measurement information indicating measurement positions on a wafer to the plurality of measurement devices.
In a similar manner, when a plurality of wafers are sequentially mounted on one measurement device, the coordinates of measurement points on the respective wafers may have different values. For example, in the case where the orientations of the wafers set in the measurement device are not accurately fixed but have arbitrary angles to some extent, the respective wafers have different coordinate values for the measurement points. Namely it is rather difficult to accurately determine the positions of the measurement points even in one measurement device.
One object of the present invention is to provide a technique of commonly applying measurement information indicating measurement positions on a wafer to a plurality of measurement devices.
Another object is to provide a technique of determining the positions of measurement points on a wafer based on such measurement information.
In order to attain at least part of the above and other objects of the present invention, there is provided a method of determining a measurement position on a semiconductor wafer mounted on a stage of a measuring device. The method comprises the steps of: providing measurement information regarding a plurality of measurement points on the wafer, wherein the measurement information includes at least positions of the measurement points on the wafer, and wherein the position of each measurement point is expressed by coordinates in a wafer coordinate system defined on the wafer; and determining a position of each measurement point on the wafer mounted on the stage on the basis of the measurement information.
Since the position of each measurement point is expressed by coordinates in the wafer coordinate system, the measurement information including positions can be commonly applied to a plurality of measurement devices. Even when it is difficult to mount a wafer on the stage the measurement device at a constant position and orientation, the measurement information can be used for determining the positions of the measurement points on each wafer.
The step of determining a position of each measurement point may comprise the steps of: (a) providing first transform coefficients for coordinate transformation between a stage coordinate system defined on the stage and the wafer coordinate system; (b) transforming coordinates of each measurement point in the wafer coordinate system which are included in the measurement information into first coordinates in the stage coordinate system using the first transform coefficients; and (c) positioning each measurement point on the wafer mounted on the stage using the first coordinates of each measurement point in the stage coordinate system.
The measuring device may comprise an image pickup device for capturing an image on the wafer mounted on the stage. In this case, the step (a) may comprise the step of providing second transform coefficients for coordinate transformation between the stage coordinate system and an image coordinate system defined within an image captured by the image pickup device; and the step (c) may comprise the steps of: i) moving the image pickup device according to the first coordinates in the stage coordinate system obtained at step (b); ii) capturing an image by the stage coordinate system; iii) determining coordinates of each measurement point in the image coordinate system; iv) transform coordinates in the image coordinate system into second coordinates in the stage coordinate system using the second transform coefficients; and v) positioning each measurement point on the wafer mounted on the stage according to the second coordinates of each measurement point in the stage coordinate system.
Even when the image coordinate system is inclined to the stage coordinate system, this arrangement enables the coordinates of an arbitrary point in the captured image to be determined accurately in the stage coordinate system.
The measurement information may further include a template image and a positional offset between a reference point of the template image and each measurement point, wherein the template image is to be used to determine the position of each measurement point by carrying out pattern matching on an image captured by the image pickup device. The step iii) may comprises the steps of: carrying out the pattern matching on the image captured by the image pickup device in the vicinity of each measurement point to obtain a matching pattern that matches the template image; and determining the position of each measurement point from a position of a reference point of the matching pattern and the positional offset.
The pattern matching using the template image determines the position of each measurement point with a high accuracy.
The measurement information may further include measurement conditions at each measurement point, and the method may further comprise the step of: carrying out measurement at each measurement point under the measurement conditions.
The present invention is also directed to a measuring device for determining a measurement position on a semiconductor wafer mounted on a stage of the measuring device. The device comprising: a memory for storing measurement information regarding a plurality of measurement points on the wafer, wherein the measurement information includes at least positions of the measurement points on the wafer, the position of each measurement point being expressed by coordinates in a wafer coordinate system defined on the wafer; and a position determination unit which determines a position of each measurement point on the wafer mounted on the stage on the basis of the measurement information.
The present invention is further directed to a computer program product for determining a measurement position on a semiconductor wafer mounted on a stage of a measuring device. The computer program product comprises: a computer readable medium; and a computer program stored on the computer readable medium. The computer program comprises: a first program for causing a computer to obtain measurement information regarding a plurality of measurement points on the wafer, wherein the measurement information includes at least positions of the measurement points on the wafer, the position of each measurement point being expressed by coordinates in a wafer coordinate system defined on the wafer; and a second program for causing the computer to determine a position of each measurement point on the wafer mounted on the stage on the basis of the measurement information.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.